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Wednesday, January 29, 2014

Less Is Sometimes More: Roche Brain Shuttle Technology for Drug Delivery into CNS

After Roche and ISIS Pharmaceuticals announced last April that a co-development effort to apply Roche’s Brain Shuttle technology for the
systemic delivery of antisense oligos would form part of their Huntington’s collaboration,
I started to pay some attention to this technology. This is because despite the already enormous
promise of Oligonucleotide Therapeutics for CNS disorders (think of all the neurodegenerative
diseases) with the direct administration of single-stranded oligonucleotides into the CNS,
its value could be further enhanced with a systemic delivery approach such as
the Brain Shuttle tech.

This is not only because intravenous administration methods
would be preferable over the more invasive direct intra-CNS
injections/infusions, but also because a systemic delivery approach promises a
more uniform drug distribution and would minimize the importance of diffusion. It
is the limited diffusion of current RNAi delivery techs that is holding back
RNAi Therapeutics in this important therapeutic area.

The fundamental principle behind Brain Shuttle is actually not that novel at
all. Companies like Armagen have long attempted to target receptors such as the
insulin receptor and the transferrin receptor on brain capillary endothelial
cells as in normal physiology these receptors function to shuttle
transferrin/iron and insulin across the notoriously recalcitrant blood-brain-barrier.

Based on newly published data by Roche scientists (Niewoehner et al. 2014), a conventional antibody approach does not work. To wit, a conventional antibody consists of
two binding sites (divalent) and such engagement apparently causes receptor trafficking to be
re-directed to the degradative lysosome compartment of the brain endothelial
cells, at least in the case of the transferrin receptor tested. By contrast, when receptor targeting occurs
via monovalent interaction, the normal receptor physiology, including
transcytosis, is maintained. Using this
strategy, it was shown that the intra-parenchymal delivery, i.e. delivery into the brain proper, of an antibody
against beta-amyloid (related to Alzheimer’s disease) that had been tethered to the
monovalent transferrin receptor antibody was enhanced on the order of 50-fold.

The way how this research can be translated into RNAi Therapeutics is to simply append an RNAi trigger instead of the beta-amyloid antibody to the transferrin receptor antibody. Or you could do away with
proteins altogether and replace the transferrin receptor antibody with an
aptamer-RNAi trigger combo (e.g. a Dicer-substrate in the spirit of tomorrows IPO by Dicerna Pharmaceuticals). Hence, the irony of the ISIS-Roche delivery
collaboration is that ISIS could- to put it just slightly hyperbolically- be shoveling
its own grave by eroding the current advantage of phosphorothioate antisense
over RNAi for gene knockdown in the CNS.

I have to view your comments as off-base and slanted Mr. Dirk. Roche has had a good education into RNAi relatively speaking for a big pharma. They choose ISIS ANS technology over anything RNAi. There are subtleties that we as bystanders don't know about the brain shuttle technology that may very well have caused their move in that direction. It is my belief that you never really give ISIS or their ANS technology any credit and that your views are slanted by old experience with ANS and some personal vendetta against ISIS and Dr. Crooke. The bringing of RNAi into a cell via the brain shuttle may very well have bigger problems than you envision. The cost may very well be much higher as well. The basic premise of ANS in neurodegenerative diseases isn't just their being given intrathecally or being able to cross the BBB via this brain shuttle, it has to do with their ability to get their payload into the nucleus. Unless you bring your own Dicer system into the nucleus with you I don't see of what value dsRNAi strands will have. The single-strandedness of the technology of ANS is not as powerful in your own mind, but that single strand may very well be the elegance as to what you need to treat neurodegerative diseases(an orthopedic surgeon can pound out bone faster than a neurosurgeon...but that isn't always desirable. Also, that increased volume from an RNAi strand in the nucleus may very well clog things up biochemically. Possibly in a way like fluorquinolones do when the inhibit topoisomerases and what they do when they don't allow the DNA to recoil back up. Time will tell, but I wouldn't underestimate Roche even if you will always underestimate ISIS and their brand of ANS. t

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